A number of studies have demonstrated the necessity of the hippocampus in learning spatial tasks, as well as tasks requiring the association of temporally remote events. In addition to demonstrating that an intact hippocampus is required for acquisition of these tasks, several studies have indicated that animals with dorsal hippocampus (DH) lesions are impaired in learning the water maze task; animals with ventral hippocampus (VH) lesions show no impairment. To date, no study has sought to systematically determine which hippocampal region(s) is required for learning tasks requiring the association of temporally remote events. This proposal seeks to identify the necessary region(s) of the hippocampus for acquisition of trace eyeblink conditioning (EBC), a temporal associative task. It is hypothesized that the DH, VH or entire hippocampus are equally likely to be involved in learning trace EBC. This proposal also seeks to determine if a common cellular mechanism underlies acquisition of different hippocampally- dependent tasks. Previous work done by our laboratory has shown reduced post-burst afterhyperpolarization (AHP) and spike frequency accommodation in CA1 hippocampal neurons from rabbits that have acquired trace EBC. These changes were learning specific. This proposal seeks to determine if acquisition of another hippocampally-dependent task, Morris water maze, results in a similar reduction in AHP. In addition, the effects of simultaneous training on these two tasks on neuronal excitability will be assessed. It is hypothesized that training on water maze will cause a similar reduction in AHP as is seen following trace EBC, and following simultaneous training on these two tasks either an even greater reduction in AHP in individual neurons will be seen, or a greater percentage of CA1 neurons will exhibit a reduction. Rats will be used instead of rabbits in this study since alternative learning tasks, such as the water maze, have been developed for this species: Thus, how the hippocampus encodes information on both a regional as well as cellular level, will be explored in this proposal.